The genetic variability of human immunodeficiency virus type 1 (HIV-1), which is greatest in the envelope gene, affects its biological properties, including growth in different cell types, cytopathicity, and recognition by neutralizing antibodies and cytotoxic T-cells. This variability has obvious implications for vaccine design. Work has continued on identification and characterization of broadly reactive neutralizing epitopes and how they are affected by variation. Several infectious DNA clones of the MN strain of HIV-1 have been constructed to further elucidate the contribution of the V3 loop of gp120 to recognition by natural neutralizing antibodies. Nigerian HIV-1 strains have been identified as belonging predominantly to the G clade. HIV-1 strains isolated from males and females from St. Petersburg, Russia, have been identified as being of the B clade common in North America and Europe. Earlier isolates from Russian women were primarily of African subtypes; detection of clade B HIV-1 may signal a change in epidemiologic patterns in Russia. A study of long-term infected nonprogressors has shown that the presence of a complete nef gene does not necessarily lead to disease progression. An HIV-1(IIIB) host range variant able to grow on epithelioid cells has been characterized; part of this ability appears to be conferred by the gag gene. Several advances have been achieved in the area of recombinant antibodies. Libraries of recombinant antibodies have been obtained from lymph node RNA of HIV-1-infected individuals and several categories or neutralizing antibodies have been obtained and are being characterized. The range of strains recognized by recombinant neutralizing antibodies have been successfully broadened by substitution of heterologous light chains to create hybrid antibodies.